Apparatus for Reading a Color Symbol

ABSTRACT

The present invention provides an apparatus for reading a color symbol, which comprises a matrix of color filters arranged in front of a detector. Light received from the filters of some colors is used to locate the color symbol, while light received from all the filters is used to read and decode the located symbol. Preferably, the filters used for locating the symbol are of the colors to which the detector is most sensitive. Preferably, the filters for locating the symbol are dominant in number.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application to U.S. patentapplication Ser. No. 10/996,802, filed Nov. 24, 2004, now issued as U.S.Pat. No. 7,124,957, granted Oct. 24, 2006, and U.S. patent applicationSer. No. 11/551,918, filed Oct. 23, 2006, now allowed, the disclosuresof which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to symbol reading and decoding techniques,and more particularly, to apparatus for reading color symbols, such ascolor one and two dimensional barcodes, with higher sensitivity andresolution.

BACKGROUND OF THE INVENTION

Barcodes, with various desired information encoded therein, areuniversally used in many circumstances. There are many types ofbarcodes, such as 1-D barcodes stacked barcodes, 2-D barcodes, etc.These barcodes are usually monochrome symbols that are encoded withinformation in specified patterns of barcode elements (or cells) of twosharply contrasted colors such as black and white. To increase the“information density” (i.e., the information included in the limitedsymbol area), various colors are also used as the barcode elements as incolor barcodes. The color barcodes are usually also read by monochromereaders which identify different colors by different levels ofelectrical signals generated from light reflected from the symbolelements of different colors. However, the sensitivity and resolution ofreading color symbols by monochrome readers is not satisfactory,especially when the color symbols are buried in a colorful backgroundsuch as a color picture.

One technique of reading such color symbols employs plural primary colorfilters, such as Red-Green-Blue filters. A drawback of such anarrangement is that significant loss of sensitivity results from thefiltering of the light reflected from the symbol.

Therefore, there exists a need for a reading system that can read acolor symbol with high sensitivity and resolution, even if the colorsymbol is buried in a colorful background.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for reading a color symbol,which comprises a matrix of color filters provided in front of adetector. According to the teachings of the present invention, lightreceived from the filters of some colors is used to locate the colorsymbol, while light received from other filters or all the filters isused to read and decode the located symbol.

Preferably, the colors of the filters used for locating the symbol arein the range of wavelengths at which the detector is most sensitive.Preferably, the filters for locating the symbol are of the same color,which is preferably of a wavelength of the detector.

Preferably, the pattern of the filters for locating the symbol is of azigzag pattern, which is a part of the whole filter matrix.

Preferably, one color of filters is used to locate the symbol, and allthe filters are used to decode it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an exemplary color symbol readingsystem according the concept of the present invention;

FIG. 2 illustrates a matrix of filters of an embodiment according to thepresent invention; and

FIG. 3 illustrates a zigzag line resulted from the zigzag pattern of thedominant color filters in the matrix of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the color symbol reading apparatus according to thepresent invention is schematically illustrated in FIG. 1, whichgenerally comprises a light source 14 (such as LED) for projecting light1 to a color symbol (such as a color barcode) 20, a detector 11 forreceiving light 2 reflected from the symbol 20 and for generatingelectrical signals from the received reflectance light 2, an amplifiercircuitry 12 for amplifying the signals generated by the detector 12,and a decoding circuit 13 for decoding the amplified electrical signalsreceived from the amplifier circuitry 12 to obtain a reading result.

According to the present invention, a color filter array (CFA) or filtermatrix 10 which comprises filters of various colors is provided in frontof the detector 11 for filtering the reflectance light 2 before it isreceived by the detector 11. Only the light passing the filters of some(but not all) colors are utilized to locate the color symbol 20, whilethe light passing all the filters are utilized to read and decode thesymbol 20.

An exemplary embodiment of the filter matrix 10 is illustrated in FIG.2, which comprises filters of three different colors, i.e., the threecomponent colors Cyan, Yellow, Magenta of CYM color system, which isexpected to pass through more light than RGB filter system. In FIG. 2,yellow filters are represented by “white” squares 15, cyan filters by“gray” squares 16, and magenta filters by “dark” squares 17. Forclarity, only some of the filters are designated by reference numbers15, 16 and 17.

Noticeably in FIG. 2, yellow filters 15 are dominant in numberthroughout the area of the filter matrix 10. In the example here, thereare twice as many filters of yellow color as of each of the other twocolors. The yellow filters 15 subtract blue color in principle and passother spectrum of light onto the detector 11. In this preferredembodiment, the reflectance light 2 that passes the yellow filters 15 tobe received by the detector 11 is utilized to locate the colored symbol20. The symbol 20 is located as a whole symbol block but not by symbolelements. In this embodiment, detector 11 has a dominant sensitivity forthe colors passing through the yellow filter. Thus, a high sensitivityof the detector in locating the color symbol 20 is achieved.

After the color symbol 20 is located by the light 2 passing the yellowfilters 15, the light 2 that passes all the color filters 15, 16 and 17in the filter matrix 10 is utilized to read and decode the coloredsymbol 20, which achieves a higher resolution as compared to prior colorsymbol readers.

In order to calculate run-length with minimum noise, pixels of the samecolor should be used. To this end, as illustrated in FIG. 2, thedominant yellow filters 15 are preferably arranged in the filter matrixin a zigzag pattern both horizontally and vertically. This generates azigzag line 15 a (see FIG. 3) for calculating run-length with minimumnoise. Once a finder of the barcode or color symbol 20 is found, thecolors of the symbol 20 can be then evaluated, which is useful forremaining processing of the symbol 20.

Though the yellow filters 15 are utilized as the dominant color filtersin the preferred embodiment illustrated in FIG. 2, any other color (suchas cyan or magenta) may also be used as a dominant color to locate thecolored symbol 20. Preferably, the detector 11 has the most sensitivityfor the wavelength of the same color of the dominant color filter, or isthe most sensitive to the color of the dominant color filters.

Other color systems can also be utilized. For example, filters can havered, green and blue colors as in an RGB color system, with one (e.g.,red) of the colors as the color of the dominant filters for locating thesymbol 20. Filter matrices containing more than three types of filterscould also be employed. It is desirable, although not critical to thepresent invention, that the wavelength at which the detector 11 is mostsensitive and the filter used to locate the symbol have similarwavelengths, in order to maximize the sensitivity.

Alternatively, the matrix filters 10 may comprise more than three colorsand the filters for locating the symbol 20 may comprise more than onecolor (such as yellow in FIG. 2). For example, the filters for locatingthe symbol 20 may comprise filters of several different colors. If so,the colors are preferably close to each other and the detector 11 ismore sensitive to them than other colors.

Though the above describes the preferred embodiments of the presentinvention, it will be appreciated that, without departing the spirit ofthe present invention, numerous adaptations, variations andmodifications are readily available to a person with ordinary skill inthe art. For example, the color filters 15, 16, 17 can be of other typesof patterns other than that shown in FIG. 2, such as honeycomb pattern.The color symbol 20 can be a linear barcode of any dimension, a stackedbarcode, a matrix barcode, etc., buried in a colorful background or not.The filters used for locating the color symbol 20 may or may not bedominant in number as compared to other filters. Therefore, the scope ofthe present invention is intended to be solely defined in theaccompanying claims.

1. Apparatus for reading a colored symbol comprising a matrix of filtersof at least two different wavelengths of light placed in front of adetector, wherein a majority of the filters filter a dominant colorsubstantially equal to a wavelength of said detector.
 2. Apparatus ofclaim 1 wherein a wavelength reflected by the colored symbol issubstantially equal to the wavelength of said detector.
 3. Apparatus ofclaim 1 wherein the matrix of filters comprises a majority of filterssubstantially equal to the wavelength of said detector.
 4. Apparatus ofclaim 1 comprising at least three filters of different wavelengths. 5.Apparatus of claim 2 wherein said wavelengths are of the color Cyan,Magenta, and Yellow.
 6. Apparatus of claim 2 wherein said wavelengthsare of the color Red, Green, and Blue.
 7. A method of locating andreading a symbol comprising locating the symbol by detecting lightthrough filters arranged in a first pattern, and reading the symbol bydetecting light through filters arranged in a second pattern.
 8. Amethod of locating and reading a color symbol from a pattern, saidmethod comprising using a matrix of filters of at least three differentcolors, wherein light passing through filters of a first color is usedto locate the color symbol, and light passing through of a second andthird color is used to read the symbol.
 9. The method of claim 8 whereinat least one of said colors is yellow.
 10. The method of claim 8 whereinfilters of the first color are approximately equal in number to filtersof the second and third colors combined.
 11. The method of claim 8wherein filters of the first color are arranged in a zig-zag pattern.